What could be the keystone habit for people who want to lose weight? Is it strict dieting? Joining a gym? Or perhaps altering daily routines, such as opting to take the stairs instead of the elevator? The long-term effectiveness of these methods tends to be minimal. After an initial burst of enthusiasm fades by the end of the month, people often revert to their old eating habits and sedentary lifestyles.

The 2009 study, funded by the National Institutes of Health and involving a cohort of 1600 individuals categorized as obese, investigated a novel weight loss approach. The participants were instructed to engage in the task of recording detailed information about their dietary intake, specifically documenting everything they consumed…

…at least one day per week. It was hard at first. The subjects forgot to carry their food journals, or would snack and not note it. Slowly, however, people started recording their meals once a week—and sometimes, more often. Many participants started keeping a daily food log. Eventually, it became a habit. Then, something unexpected happened. The participants started looking at their entries and finding patterns they didn’t know existed. Some noticed they always seemed to snack at about 10 A.M., so they began keeping an apple or banana on their desks for midmorning munchies. Others started using their journals to plan future menus, and when dinner rolled around, they ate the healthy meal they had written down, rather than junk food from the fridge. The researchers hadn’t suggested any of these behaviors. They had simply asked everyone to write down what they ate once a week. But this keystone habit —food journaling—created a structure that helped other habits to flourish. Six months into the study, people who kept daily food records had lost twice as much weight as everyone else. “After a while, the journal got inside my head,” one person told me. “I started thinking about meals differently. It gave me a system for thinking about food without becoming depressed.” 

Charles Duhigg